A fuel cell system, which has been placed in practical use, directly converts energy of hydrogen gas into electric energy using electrochemical reaction that occurs in the fuel cell. Therefore, the fuel cell system can obtain electric energy with high conversion efficiency. In this type of fuel cell system, it is necessary to continue to supply hydrogen gas to the fuel cell from a conduit connected to the fuel cell. Since supply of hydrogen gas is important, it is necessary to monitor whether there is leak of hydrogen gas or blockage in the conduit.
As a technology for detecting such leak of hydrogen gas or blockage, there is known a technology in which pressure sensors are provided at plural portions in the conduit connected to the fuel cell, and a pressure value detected by each of the pressure sensors is compared with a reference pressure value that is set at each of the portions at which the pressure sensors are provided (Japanese Patent Laid-Open Publication No. JP-A-3-250564). With this configuration, it is possible to detect gas leak or blockage at each of intervals between plural pressure sensors.
However, in the case where detection is performed only by comparing the measured pressure value and the reference pressure value that is a value at a normal time as disclosed in the aforementioned Japanese Patent Laid-Open Publication No. JP-A-3-250564, it may be wrongly detected that there is gas leak when there is no gas leak. The reason why wrong detection may be made is as follows. Since hydrogen permeates through an electrolyte membrane constituting the fuel cell, a decrease in pressure on a hydrogen electrode side inevitably occurs, and it is difficult to distinguish between this decrease in pressure and a decrease in pressure due to a hole in the electrolyte membrane.